A vehicle air bag assembly functions to protect a vehicle occupant during a crash or collision. A typical vehicle air bag assembly comprises a container, an inflatable air bag disposed in the container, and an inflator in proximity to the inflatable air bag. At the onset of a collision, the inflator is actuated and rapidly directs an inert, non-toxic fluid, such as nitrogen gas, into the air bag. The fluid forces the air bag out of the container and rapidly inflates the air bag into a predetermined three-dimensional configuration. On the driver side of a vehicle, an air bag assembly is commonly incorporated into the vehicle steering wheel and the predetermined configuration of the air bag will usually approximate the shape of an ellipsoid.
A method of making an air bag will generally include the step of forming a set of air bag panels and joining these panels together to form a structure capable of being inflated to a three-dimensional configuration. For example, a driver side air bag is commonly made by forming front and rear circular panels and joining these panels together around their circumferential (or perimetric) edges. The front panel forms an occupant impact area when the air bag is expanded to its predetermined configuration. The rear panel includes a mouth which defines an inflation fluid inlet opening and which may be attached to the container and/or the inflator. Other panels may also be appropriately incorporated into the air bag, such as vent reinforcement panels, mouth reinforcement panels, heat shield panels, and/or strap panels.
A plurality of sets of air bag panels may be efficiently formed with a die-cutting system. A typical die-cutting system includes a conveying assembly, a fabric dispensing assembly, and a press assembly, all of which coordinate with one or more die boards to form the air bag panels. For example, to form a plurality of sets of driver side air bag panels, a first die board and a second die board would be provided. The first die board would include a plurality (typically ten or more) of straight edge knives, each corresponding to the desired shape of the front panel. ("Straight" in this context corresponds to a contour which is non-undulant rather than strictly linear. Thus, the overall geometry of a straight edge knife could be circular.) The second die board would include an equal number of circular straight edge knives, each corresponding to the desired shape of the rear panel. These die boards sometimes also include additional straight edge knives for forming other air bag panels, such as vent reinforcement panels, mouth reinforcement panels, and/or heat shield panels.
To form the air bag panels, a roll of fabric is loaded onto the fabric dispensing assembly and a die board is appropriately placed onto the conveying assembly. The fabric dispensing assembly then loads a desired number of layers of the fabric (typically fifteen or more) onto the die board. Thereafter, the conveying assembly and the press assembly coordinate to apply pressure on the fabric layers to die-cut the air bag panels. The panels are then unloaded from the die board and transported to a location where subsequent assembly steps may be performed.
One may appreciate that such a die-cutting system can be used to mass-produce air bag panels efficiently. For example, if a die board includes ten rear panel knives and fifteen layers of fabric are loaded onto the die board, one hundred-fifty rear air bag panels may be simultaneously produced. Thus, producing air bag panels with a die-cutting system can be very advantageous from a production time standpoint. Moreover, many air bag manufacturers have invested in, and their facilities are designed to accommodate, such die-cutting systems.
In the past, air bags panels have usually been formed from a woven synthetic fabric, such as nylon, which is coated with a material such as neoprene. With particular reference to a driver side air bag, both the front panel and the rear panel have been formed from such a coated fabric. The coated fabric insures that the air bag panels formed from the fabric will be resistant to heat and will be essentially impermeable by fluids and/or particles released or produced during the inflation process. Additionally, the coated fabric inhibits the fraying of the straight edges of the air bag panels. Such fraying is undesirable because it could negatively affect the structural integrity of the air bag and/or complicate intermediate assembly steps.
Applicants believe that a driver's side air bag may include a rear panel in which the heat resistance and the fluid impermeability qualities of a coated fabric are not necessary. Consequently, applicants believe that an uncoated fabric could be used to form this rear panel. Because uncoated fabrics are generally less expensive than coated fabrics, the use of an uncoated fabric to form the rear panel would reduce the cost of the air bag. However, applicants also appreciate that the rear panels produced in existing die-cutting systems have circumferential (or perimetric) edges which have straight contours. Applicants believe that if the rear panels were formed from uncoated fabric in these die-cutting systems, their straight edges would have a tendency to fray during subsequent assembly steps and/or in the completed air bag. Accordingly, applicants believe that the use of a coated fabric is still necessary to form rear air bag panels with conventional die-cutting systems.
Applicants believe that a laser-cutting system could possibly be used to form rear air bag panels from an uncoated fabric because a laser-cutting system would heat seal the edges of the panels during the cutting process. This heat sealing would minimize the tendency of the circumferential edge of the rear panel to fray. However, the capital investment for a laser cutting system is quite significant and would require the replacement or abandonment of existing die-cutting equipment. Additionally, only five or six panels may be produced at a time with most laser cutting systems thereby making them uncompetitive, from a production time standpoint, with conventional die-cutting systems.
The present invention provides a method of making air bags which allows at least some of the air bag panels to be formed from uncoated fabrics. The method is competitive with conventional die-cutting techniques from a production time standpoint and does not require a significant capital investment in machinery. In the preferred embodiment, the method is used to form certain panels for a driver side air bag. However, the invention may also be applicable to the manufacture of certain passenger side air bag panels. Moreover, as uncoated fabrics with sufficient heat resistance and fluid impermeability qualities are developed, the method may be used to produce any or all of the panels in both driver side and passenger side air bags.
More particularly, the present invention provides a method of making air bags for vehicle air bag assemblies. The method comprises the step of forming a set of air bag panels which includes a first panel with a perimetric edge and a second panel with a perimetric edge having an undulant fray-inhibiting contour. The air bag panels are joined together to form a structure capable of being inflated to a predetermined three-dimensional configuration. Specifically, the perimetric edges of the first and second panels are joined together. The fray-inhibiting contour of the second panel's perimetric edge, which is preferably a pinked contour, prevents the fraying of this edge. In this manner, the second panel may be formed from an uncoated fabric without affecting the structural integrity of the air bag and/or complicating intermediate assembly steps.
Preferably, a plurality of second panels are simultaneously formed by die-cutting them with a specially designed die-board. The die board includes a series of knives, each of which has a shape corresponding to the desired shape of the second panels and the desired undulant fray-inhibiting contour. Consequently, the present method may be practiced with existing die-cutting systems simply by providing an appropriate die board. Additionally, the production rate of this method will be approximately the same as the production rate of conventional die-cutting techniques.
The present invention also provides an air bag for a vehicle air bag assembly which includes a set of panels joined together to form a structure capable of being inflated into a predetermined three-dimensional configuration. The set of air bag panels includes a first panel with a perimetric edge and a second panel with a perimetric edge having an undulant fray-inhibiting contour. The perimetric edges of these first and second panels are joined together. Preferably, the air bag is for a driver side air bag assembly and the predetermined configuration is an ellipsoid shape. In this preferred embodiment, the set of panels includes a circular front panel which is made from a coated fabric and a circular rear panel which is made from an uncoated fabric and which has a circumferential edge having an undulant fray-inhibiting contour.